The field of the present invention is power systems for small vehicles.
Small vehicles straddled by a rider and having three or four wheels particularly adapted for over-land use have found popularity. The configuration of such vehicles has typically included a frame with an engine located within the frame, often under the seat. The rider straddles the vehicle with his feet on footpegs extending laterally from the frame. A steering handlebar controls the direction of the vehicle.
With such over-land vehicles, drive of all wheels is often desired. However, the design of the drive system for driving all wheels faces certain complications when applied to a straddle-ridden vehicle. One major difficulty is the achievement of proper power train compactness. The lateral dimension of the vehicle where straddled by the rider is limited by the size of the rider. The footpegs cannot be so placed that the rider position becomes awkward. The ability of the rider to control the stability of the vehicle in part by his own weight requires that the footpegs be properly located. As a result, the power train located generally beneath the rider and between the footpegs cannot be excessively wide.
For purposes of vehicle clearance, unencumbered steering and reduced overall length, the longitudinal size of the engine is advantageously kept to a minimum. Naturally, mechanical simplicity is also advantageous.
Two systems previously devised employing all-wheel drive are disclosed in Japanese Pat. Nos. 44-4694 (1969) and 49-6923 (1974). In the former, a shaft drive for the front wheels is connected to an output shaft providing power to the rear wheels. In the latter, a chain drive for the front wheels is connected to the rear wheel output shaft as well. Such systems require the output shaft to be located to the side of the crankcase and in such a location as to have a direct line to both the front and rear axles. Consequently, the engine width becomes excessive. As a result, space is restricted and the footpegs may be inappropriately placed. The same difficulty is naturally applicable to all-wheel drives on both motor tricycles and four-wheel vehicles.